As for a power semiconductor element, to protect it from an overheat breakdown, measures are taken for detecting the temperature of the semiconductor element and controlling the semiconductor gate in response to the detection (see Patent Document 1, for example). In addition, the temperature detected is transferred to an external apparatus to be displayed thereon via an interface with the outside. Since a power semiconductor element operates under a high voltage/high current environment, the communication with the outside usually employs a contactless means. Although the Patent Document 1 shows an example of contactless transmission using an antenna, a contactless transmission means such as a photocoupler is generally used. In addition, if the temperature detected is high, measures are generally taken to stop the gate driving of the semiconductor element to prevent a thermal breakdown of the semiconductor element. The Patent Document 1 also shows an example that makes a direct decision of a temperature detection result, and breaks the gate driving signal.